Nicene and Post-Nicene Fathers, Vol. II:
City of God: Chapter 8

Chapter 8.—That the Saints, by Suffering the First Death for the Truth’s Sake, are Freed from the Second.

For if we look at the matter a little more carefully, we shall see that even when a man dies faithfully and laudably for the truth’s sake, it is still death he is avoiding.  For he submits to some part of death, for the very purpose of avoiding the whole, and the second and eternal death over and above.  He submits to the separation of soul and body, lest the soul be separated both from God and from the body, and so the whole first death be completed, and the second death receive him everlastingly.  Wherefore death is indeed, as I said, good to none while it is being actually suffered, and while it is subduing the dying to its power; but it is meritoriously endured for the sake of retaining or winning what is good.  And regarding what happens after death, it is no absurdity to say that death is good to the good, and evil to the evil.  For the disembodied spirits of the just are at rest; but those of the wicked suffer punishment till their bodies rise again,—those of the just to life everlasting, and of the others to death eternal, which is called the second death.